Door-lock systems which are equipped with a lock device for vehicle doors for enabling locking and unlocking of vehicle doors by driver's key operation or the like are applied to most vehicles. In recent years, a door lock system which is capable of locking and unlocking of doors when a user carrying a portable device touches a contact detection device installed on a door handle is widely mounted. A door-lock system is one of security devices used to prevent theft of or from a vehicle. Other security devices mounted on vehicles include steering lock systems and immobilizer systems. One example of contact detection devices applicable to a door lock system or the like is an electrostatic capacitance sensor which is provided with a pair of electrodes used as a touch area that a subject touches and is capable of sensing a change in electrostatic capacitance.
A contact detection device such as the electrostatic capacitance sensor is generally provided with a sensor electrode mounted on a door handle. However, as the door handle may be come into contact with raindrops or the like, there is a risk that such a contact made by raindrops or the like is erroneously detected as a touch of user. As described above, the electrostatic capacitance sensors are sensors which detect a change in electrostatic capacitance. The electrostatic capacitance sensors are configured to capture the change in electrostatic capacitance caused by stray electrostatic capacitance of the human body. Therefore, because the electrostatic capacitance also changes due to stray electrostatic capacitance of raindrops, there are occasions when it is impossible to determine whether or not a touch is human-induced.
In light of such a situation, some systems have been developed in order to prevent an erroneous detection by an electrostatic capacitance sensor or the like due to raindrops or other factors. For Example, JP 2002-57564A discloses a human body detector including an electrostatic capacitance sensor that a human body touches, and a detecting unit that receives an output from the electrostatic capacitance sensor and distinguishes between a human body and raindrops to detect only a human body. It is also disclosed in JP 2002-57564A that the sensor unit performs the distinction between a human body and raindrops to detect only a human body by receiving the output from the electrostatic capacitance sensor based on a change in the output within a predefined time period.
Further, JP 6-162888A discloses a non-contact switch including a sensing unit having a sensor element in which a pair of electrodes are arranged close to each other on a substantially single plane, and a sensor circuit that outputs a detection signal when electrostatic capacitance between both of the electrodes decreases below a reference value when a human body comes closer. The sensing unit is configured such that a main sensor element is surrounded by multiple sensor elements. The sensor circuit includes a sensor unit that generates a detection signal for each of the sensor elements and a determination unit that generates an output signal only when a detection signal corresponding to the main sensor element is generated and the detection signal is not followed by another detection signal corresponding to another sensor element within a predefined time period.